Process for the manufacture of laminates



Patented Nov. 10, 1953 Joseph-U; ram; lios -Angeles; Caliit, assignorto Agrashelkllnc ;LossAngeles, Calif., a corpora tionsoflllelaware No Drawing. ApplicationJuly 18,1950,

SeriaLNo. 174,580 v This invention relates to themanufactureof laminates'including plywoodandmore specifically: to a gluing procedure in theproduction of lamie. nates involvinga process-capable ofutilizingrzmore highly filled phenol-formaldehyde glue mixes;

Under present commercial practice; plywood? of 'two principal types are produced, namely all"-- weather plywood and' interior plywood-' from" either hardwood or-softwood'. The formerem.-

ploys substantiallyexclusively aphenol-former dehyderesin glue emulsion which is. relatively expensive as-compared tothe cost: of" other plywood glues; Interior-plywoods are preparedtal' 7 mostexclusively from proteinous gluesrand the:

boards produced therefrom. do not" possess the greater strength :and' high weatherand?mold= resistant properties ofthe-exterionplywood: The

glue mixesused for both types. ofi plywood are composed of glue, aligno-cellulose or othen-ex+.. tender-and water.

It has been realized forsometime that it" is highly desirable to find some: means; whereby plywoodfor interior use can be produced-utilize: ing phenol=formaldehyde resin glueseatt a price comparable tothat. at which the interior-ply.

wood is prepared; Several: operators: lieretoforeij to-the-time the pliesare assembled forloadinginto steam heated platen presses for final'curing,

isone ofthese units which must be operated-on" a carefully I controlled time schedule;

The glue mix must possessa-number-of properties under constant control. Itmust remain tacky for'the periodrequired for assemblingthe plies and it-mustcure andset rapidlyto-provide for hardening within the required curing-time cycle. The glue-mix also must remain at a-constant consistency sufiicientto avoid any'appreciable variation in the-thickness of the gl-ue film applied as the consumption of the batch of'glue proceeds. Therefore, veryrlittle variation in the resin-extender-water ratio has.:.been permissible.

The conventional glue mix for producingexe The gl-uespreading-machine which applies the glue mix to--the surface of the prepared"boards'prion 2 terior plywood is composed of phenol formal dehyde resin glue emulsion (42% solid) with vegetableshell flour extender and waterin the weight ratio of 5:1:1. If'the quantity-of the-ex tender isappreciably increased, the consistency oftheglue-mix changes and becomes moreviscous and the quantity of glue applied bythe spreader increases and thus it is=not*on1'y'wastedbut rii duces the bond strength of the-plywood; If" only an amount of'wateris added to this highlye'x tended mix sufiicient to obtain the--required"con=- sistency or viscosity for initial application, the gluemix changes in consistency on the-spreader; before the glue can be applied; If still greater quantities of water' are employed-to preventthis: excess thickening, the resulting glue would 'be thrown off. the: spreader rolls due' tolow initial" viscosity, would cause the extender to separate from the resin binder and would cause'tli'e boards, toblow inthepress due to excessivesteam release.- 7 f Accordingly, an object of the present inven tion is-to provide a process forthe-productiorr of a plywood using phenol-formaldehyde resi'n glue, of "a quality superior to that-of -'co'nvention'al{ interior plywood at a cost competitive-witli -or cheaper than thecost of producing such interior plywood. bonded with proteinous glues:

In its-primary embodiment, the inventioniinvol-ves ('1) preparing aglue mix containing phenol formaldehyde resin glue and anextender" in larger proportions than has heretofore been possible-or with an amount of extender reducing the over-all cost-'ofthe glue-"mix-toa figurecor'npetiti-ve withnthat ofconventional glue mixesfor interior plywoodproduction; and:"(2)' cooling the resulting glue mix andgmaintaimngthesame at a temperaturewonfrom about "to 75F? until it is applied; to the hard or soft wood veneers" (laminae); Through this simple: procedure-bf"? temperature control; the consistency andi vi's'-- cosity requirements are retained and the straight? line productionccanzbe continuedi-as if convene tional glue-mixes were being employed under most favorable-conditions: The permissible range-0P operable temperatures variessomewhat with the nature. of the .extender'and the ratio of the same to'therresin solids of th'eglue employed. High'er extender ratios ordinarilyrequire-lowertempera tures. Aitemperature within the range of about- "to: gives best results 1 in ordinary opera tions and even-when veryrhighlyfilled resi'n mixesare being; applied. The; instant invention" independent of tli'e mannervor means byi' whichtrie gluemix is cooled to the desired temperature. It may be cooled in the conventional mixing tank, in the glue well or on the glue spreader rolls. The cooling may be accomplished through the insertion of cooling coils in the tank or well or by cooling jackets surrounding the tank or well. Instead of cooling the glue mix within said containers it may be circulated through coils immersed in a cooling medium after which it is returned to the containers. Regardless of the apparatus employed, the cooling means may be and is preferably thermostatically controlled such that the conditions are held constant throughout continuous operation.

If the cooling of the glue mix is carried out in the mixing tank, then the temperature to which it is cooled should be somewhat lower to allow for the increase in temperature which will occur during the transfer of the glue mix from the tank, through the well, over the rolls and to the boards being treated.

Experimentation has indicated that glue mixes are operable which contain proportions by weight between about to resin solids and from 15 to about 40% or more lignocellulose filler. In such mixes the remainder is water and will ordinarily be present in the amount of from to 70%.

In accordance with prior straight line production practice, it has not been practically possible or safe to employ glue mixes containing more than five-tenths of one part filler by weight for each part phenol-formaldehyde resin solids. Through the temperature control process of the present invention, satisfactory operations have been conducted employing from six-tenths to two or more parts of the filler per part resin solids.

The process of the invention is applicable to the conventional phenol-formaldehyde resin glue emulsions supplied by various manufacturers. The use with the glue of various recommended accelerators, hardeners, alkalizing agents or other aids does not prevent the advantages of the instant temperature control process from being realized.

To illustrate examples of glue mixes found suitable for use in the practice of the present process, a number of compositions are set out in the table below, the ratios given being in parts by weight. The resin employed was an aqueous emulsion of phenol-formaldehyde resin having 42% solids as Plyophen. The flour used was walnut shell flour, as Glufil.

Glue Mix Ratio Per- Oauscent he 1 Resin Solids Resin Flour Water or soaps may be resorted to in order to obtain any required initial viscosity. Furthermore, the preparation of the mixes may be facilitated by passage through a roller mill or a homogenizer or other device to assist the wetting of the filler and to obtain and maintain-better dispersion of the filler throughout the mix.

Although the present invention is directed primarily to the production of highly filled phenol-formaldehyde resin glue mixes, the cooling step of the present invention may be advantageously employed in the application of other resin glues similarly afiected by heat when highly filled. Also the process may be used in the manufacture of conventional exterior plywood .wherein the resin emulsion-extenderwater ratio is ordinarily 511:1. The proper application or utilization of this glue mix sometimes gives considerable trouble during changes in humidity and temperature occurring from day to day. The control of the temperature of this glue mix in accordance with the present procedure eliminates this diificulty.

Manufacturers of exterior plywood generally know that the ratio of binder solids in the glue mixes they employ is higher than is essential to obtain adequate bond strength, but they have not been willing to use a lesser proportion of glue in view of the difiiculties and delays encountered when the periodic changes in atmospheric moisture and temperature conditions occur. With the utilization of the process of the present invention, a greater proportion of filler can be employed Without sacrificing the high bonding qualities required of exterior plywood.

Whereas the filler preferably employed in the glue mixes of the invention is walnut shell flour, a great variety of other nut and vegetable shell flours can be used with good success. Other ligno-cellulose fillers can be used for special pur-- poses, as redwood bark flour, ligno-cellulose products derived from the manufacture of iur'- fural, and fine particle size lignin resins themselves. The temperature control procedure is effective even when inorganic fillers are employed such as fine particle size clay.

EXAMPLE A glue mix was prepared by stirring together five parts phenol-formaldehyde resin emulsion,"

two parts walnut shell flour filler and two and one-half parts water. This glue mix was placed in the reservoir of a spreader and subjected'to the action of the spreader rolls for one-half hour during which the reservoir was cooled and the glue mix maintained at a temperature of 49 F. In a test, the viscosity of the resulting mass as 25 C. was 290 centipoises as compared with 230 centipoise measured at the same temperature, of the original mix immediately after its formation. This change of 60 centipoises is in-- consequential and small in comparison with the change which occurs when no control overthe temperature is exercised.

When another batch of this same glue mix formulation was tested in the same manner except that the temperature was permitted to remain at 6-9 P. which approximates normal room temperature, its viscosity increased from 230 to 500 centipoises in the comparative tests conducted at 25 C. This increase in viscosity of 270 centipoises is high and of sufficient magnitude to prevent the glue from being employed in conventional straight line production operations.

The process of the present invention has a number of operational and economic advantages as follows:

A. Only an inconsequential change in viscosity occurs in the glue mix during the period of its application.

B. A more uniform distribution of glue mix over the veneers is obtained and the quantity of glue applied by the spreader rolls is more uniform for any given setting of the spreader rolls.

C. In those operations where adjustment of the doctor rolls of the spreader has heretofore been used as a means for compensating for viscosity changes in the glue mix, the necessity of such adjustment is eliminated.

D. A more uniform bond strength in the finished plywood is obtained for the primary reason that uneven glue spreads are eliminated.

E. The 'glue line costs are lowered due to more uniformly thin spreads.

F. Much larger quantities of filler can be employedwhich in turn effects a reduction in the glue line cost.

G. Greater quantities of water in the glue mix are permitted due to the fact that the low temperature increases the initial viscosity of the glue, and the addition of a small amount of water does not prevent the viscosity from coming within workable limits on the spreader rolls. In contrast thereto, if additional water were added to conventional glue mixes without temperature reduction the initial viscosity would be low and the glue would be thrown by centrifugal force from the high speed rolls of the spreader.

The process of the present invention is applicable to the straight line production of laminates other than plywood, as beams and a variety of specially shaped members.

It should be understood that the present invention is not limited to specific details herein given except where indicated to the contrary and that the invention extends to all equivalents which will occur to those skilled in the art upon consideration of the scope of the claims appended hereto.

I claim:

1. In the straight line production of plywood and other laminates from veneers, using a glue spreading machine having a glue reservoir, spreader and doctor rolls, the process which comprises mixing a thermosetting phenol-formaldehyde resin glue and water with a solid extender in weight proportions of 1 resin solids to .5 to about 2 of extender, cooling the resulting fusible glue mix while in said machine and maintaining its temperature at from 35 to 75 F. during the whole period the glue remains in said machine and until it is applied to the veneers whereby heat developed in the glue while in the machine is taken up and whereby satisfactory spreading qualities are retained and spreading the cooled glue on the veneers.

2. In the straight line production of plywood and other laminates from veneers, using a glue spreading machine having a glue reservoir, spreader and doctor rolls, the process which comprises mixing a thermosetting phenol-formaldehyde resin glue and water with a solid extender in weight proportions of l resin solids to from .6 to about 2 of extender, withdrawing the heat developed in the glue due to the action of the rolls, by cooling the glue in the machine and maintaining its temperature at from 35 to F. during the whole period the glue remains in the said machine and until it is applied to the veneers, whereby the viscosity of the glue in the machine is prevented from rising to a level which prevents successful application in the straight line operation, and spreading the cooled glue on the veneers.

3. In the straight line production of plywood and other laminates from veneers, using a glue spreading machine having a glue reservoir, spreader and doctor rolls, the process which comprises mixing a thermosetting phenol-formaldehyde glue, water and a nut shell flour in weight proportions of 1 resin solids to .5 to about 2 of flour, cooling the resulting fusible glue mix while in said machine and maintaining its temperature at from 35 to 75 F. during the whole period the glue remains in said machine and until it is applied to the veneers whereby heat developed in the glue while in the machine is taken'up and whereby satisfactory spreading qualities are retained and spreading the cooled glue on the veneers.

4. The process defined in claim 1 wherein the extender is a lignocellulose material.

5. The process defined in claim 1 wherein the extender is a vegetable shell material.

6. The process defined in claim 1 wherein the extender is a nut shell extender.

7. The process defined in claim 1 wherein the extender is a nut shell extender, the proportion of resin solidsto extender being in the range of 1 part of the former to .6 to about 2 parts of the latter, by weight.

8. The process defined in claim 1 with the further limitation that the temperature of the glue is maintained within the range of 45 to 55 F.

9. The'process defined in claim 2 with the further limitation that the temperature of the glue I is maintained within the range of 45 to 55 F.

JOSEPH C. PERRY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,716,665 Redman June 11, 1929 2,414,415 Rhodes Jan. 14, 1947 2,432,544 Rhodes Dec. 16, 1947 2,473,145 Hesselbart June 14, 1949 2,489,336 Spahr Nov. 29, 1949 2,574,784 Heritage Nov. 13, 1951 OTHER REFERENCES Forest Products Lab., Synthetic Resin Glues, Revised Mar. 1947, No. 1336. 

1. IN THE STRAIGHT LINE PRODUCTION OF PLYWOOD AND OTHER LAMINATES FROM VENEERS, USING A GLUE SPREADING MACHINE HAVING A GLUE RESERVOIR, SPREADER AND DOCTOR ROOLS, THE PROCESS WHICH COMPRISES MIXING A THERMOSETTING PHENOL-FORMALDEHYDE RESIN GLUE AND WATER WITH A SOLID EXTENDER IN WEIGHT PROPORTIONS OF 1 RESIN SOLIDS TO .5 TO ABOUT 2 OF EXTENDER, COOLING THE RESULTING FUSIBLE GLUE MIX WHILE IN SAID MACHINE AND MAINTAINING ITS TEMPERATURE AT FROM 35* TO 75* F. DURING THE WHOLE PERIOD THE GLUE REMAINS IN SAID MACHINE AND UNTIL IT IS APPLIED TO THE VENEERS WHEREBY HEAT DEVELOPED IN THE GLUE WHILE IN THE MACHINE IS TAKEN UP AND WHEREBY SATISFACTORY SPREADING QUALITIES ARE RETAINED AND SPREADING THE COOLED GLUE ON THE VENEERS. 